This invention relates to filter cartridges.
A known filter cartridge is described in U.S. Pat. No. 3,392,843 and has a block-like form and comprises a filter element which is folded in a zig-zag manner. Continuous band-shaped spacers are attached to both sides of the fold walls which are created by the zig-zag folding. The band-shaped spacers are of a rectangular cross-section and are in contact with the spacer facing it situated on the opposite fold wall. In this way the fold walls are kept apart at a certain fixed distance. The fold walls run parallel to one another and the medium to be filtered passes through the filter from one edge of the zig-zag folding in the direction of the edge of the zig-zag folding situated opposite it.
A drawback of this arrangement is that the effective filter surface area available during filtration is decreased by the bandwidth of the spacers. The filter efficiency and the operational life span of the filter cartridge is thus reduced. In addition the large amount of self-hardening plastic band which has to be applied to the filter element is uneconomical as a great amount of energy and time is needed to do so. This leads to a low rate of production.
The sandwich construction, fold wall - band spacer - band spacer - fold wall, means that the tolerances are added over the four walls lying in contact with each other. Moreover the material viscosity in the band spacers varies so that the spacings between the fold walls also vary. Single folds of an exact geometry are thus nearly impossible to construct and consequently the geometry of the filter cartridge is inhomogeneous. This in turn leads to variations in the pressure differences, a shorter operational life-span and a lower filtration efficiency of the filter cartridge as well as detrimental differing velocity distributions in the medium to be filtered.
In addition, the fold walls can only run parallel to one another if two adjacent fold walls facing each other be connected by a fold whose diameter is that of the spacing distance between them since the band acts as a spacer and does not allow any other solution. A continuous throughput of the medium to be filtered through the filter cartridge is therefore not possible.